Epidemiology in animals

3.  Epi = upon; Demos = people; Ology = science
 Epidemiology = science which deals with what falls upon people
 Now it is broadly used for animals and plants also
 Bridge between biomedical, social and behavioral sciences

4. • Epidemiology is a way of thinking about health – animals’ ecology
• Much more than a collection of methods – a way of using them
• Epidemiologists consider context, heterogeneity, dynamics,
inference

5.  Oxford English Dictionary
 The branch of medical science which treats of epidemics
 Kuller LH: Am J Epid
 Epidemiology is the study of "epidemics" and their prevention
 Anderson G,quoted in Rothman KJ: Modern Epidemiology
 The study of the occurrence of illness

6. Lilienfeld A: in Foundations of Epidemiology
The study of the distribution of a disease or a physiological
condition in human populations and of the factors that influence this
distribution
Last JM: A Dictionary of Epidemiology
The study of the distribution and determinants of health related
states and events in populations and the application of this study to
control of health problems

7. • Study of the health and disease of the “body politic” – the
population.
• Basic science of public health
• What causes disease?
• How does disease spread?
• What prevents disease?
• What works in controlling disease?

8. Methods for measuring the health of groups and for determining the
attributes and exposures that influence health
Study of the occurrence of disease in its natural habitat rather than the
controlled environment of the laboratory (exception: clinical trials)
Methods for the quantitative study of the distribution, variation, an
determinants of health-related outcomes in specific groups
(populations) of individuals
The application of this study to the diagnosis, treatment, and
prevention of these states or events.

9.  Provide the scientific basis to prevent disease & injury and promote health.
 Determine relative importance to establish priorities for research & action.
 Identify sections of the population at greatest risk to target interventions.
 Evaluate effectiveness of programs in improving the health of the population.
 Study natural history of disease from precursor states through clinical course
 Conduct surveillance of disease and injury occurrence in populations
 Investigate disease outbreaks

10.  Classical:
 Descriptive, observational, field, analytical, experimental,
applied, healthcare, primary care, hospital, environmental,
occupational, psycho-social, etc
 Modern:
 Risk-factor, molecular, genetic, life-course, CVD, nutritional,
cancer, disaster, etc

11.  Qualitative designs
 Quantitative designs
 Observational
 Experimental
 Building evidence

12. MEASURING DISEASE
FREQUENCY IN
POPULATIONS

13. Classifying and categorizing disease
Deciding what constitutes a case of disease in a study
Finding a source for ascertaining the cases
Defining the population at risk of disease
Defining the period of time of risk of disease
Obtaining permission to study people
Making measurements of disease frequency
Relating cases to population and time at risk

14. .
DESCRIPTIVE EPI
 Examining the distribution of a disease
in a population, and
 observing the basic features of its
distribution in terms of time, place,
and person.
 We try to formulate hypothesis, look
into associations ?
 Typical study design: health survey
ANALYTIC EPI
 Testing a specific hypothesis about
the relationship of a disease to a
specific cause,
 by conducting an epidemiologic
study that relates the exposure to the
outcome (? Cause-effect
relationship)
 Typical study designs: cohort, case-
control, experimental design

15. Descriptive Epidemiology Is A Necessary Antecedent of
Analytic Epidemiology
To undertake an analytic epidemiologic study you must first:
Know where to look
Know what to control for
Be able to formulate / test hypotheses compatible with a-
priori lab / field evidence

16.  The three factors assessed in descriptive are:
Basic triad of Descriptive epidemiology
TIME
PLACE INDIVIDUAL

17.  TIME
 Changing or stable?
 Seasonal variation.
 Clustered (epidemic) or evenly distributed (endemic)?
 Point source or propagated.
 PLACE
 Geographically restricted or widespread (pandemic)?
 Relation to environmental exposure. water or food supply.
 Multiple clusters or one?
 Individual
 Age, sex, breed
The Basic Triad Of Descriptive Epidemiology

18.  The three phenomena assessed in analytic epidemiology are:
HOST
AGENT ENVIRONMENT

19.  Biological
 micro-organisms
 Physical
 temperature, radiation, trauma, others
 Chemical
 acids, alkalis, poisons, tobacco, others
 Environmental
 nutrients in diet, allergens, others

20. Genetic endowment
Immunologic status
Individual characteristics
Individual behavior
Definitive versus intermediate (in vector-borne diseases)

21. Living conditions (housing, crowding, water supply,
refuse, sewage, etc)
Atmosphere / climate
Modes of communication: phenomena in the
environment that bring host and agent together, such
as: vector, vehicle, reservoir, etc)

22. The first integrating principle is that epidemiology is an
information science.
The second integrating principle is that epidemiology operates
within an environment of complex systems.
Third integrating principle is that epidemiology is not just a
scientific discipline but a professional practice area.
Epidemiology as a problem solving discipline: Integrating
principles

23.  Epidemiology is an information science:
 Data generated by epidemiologists is to be used for decision making.
 Epidemiology is purposive
 Methods and knowledge are to be used for the ultimate purpose of
prevention of disease, disability and death
 Epidemiology is under public scrutiny
 Information affects decisions at the public policy level, at the level of
individuals, and by health professionals. A social responsibility.

24. Decisions:
Political,
Management
Systems:
Information,
Surveillance

25.  Timeliness
 Quality
 Quantity
 Frequency
 Use for Decision Making
 Presence of Feedback Loop

26.  Sensitivity
 Predictive value positive
 Simplicity
 Flexibility
• Acceptability
• Representativeness
• Timeliness
• Reliability or precision

27.  Budget and Resource Allocation
 Jurisdiction of agencies
 Personnel selection
 Legislation

28. Efficacy – Patient Care
Effectiveness – Herd Health
Compliance
Quality Assurance
Training
Planning
Programming

29. Structure:
 Does a structure exist to implement the health care intervention
(program) and what are its characteristics?
Process:
 Is the process to implement the health care intervention (program)
working?
Outcome:
 What effect has the intervention had on the outcome(s) of interest?

30. Our etiologic investigations continue to have a focus of simple
models even if we use multivariate analyses.
Etiologic factors operate in complex systems and we need to
consider the use of a system analysis approach in investigating
etiology.
Epidemiologists, need to work at multiple levels to make the
appropriate inferences.

31.  a solid disciplinary scientific base
 requires well grounded academic preparation
 objectives within the public-social domain
 uses well defined paradigms of problem investigation, analysis, and
inferences.

32. A professional who strives to study and control the factors that
influence the occurrence of disease or health-related conditions
and events in specified populations and societies, has an
experience in population thinking and epidemiologic methods,
and is knowledgeable about public health and causal inference in
health
(Porta M, Last J, Greenland S. A Dictionary of Epidemiology, 2008)

33.  Public Health: Emphasis on disease prevention.
 Clinical Medicine: Emphasis on disease classification and diagnosis.
 Pathophysiology: need to understand basic biological mechanisms in
disease.
 Statistics: need to quantify disease frequency and its relationships to
antecedents.
 Social Sciences: need to understand the social context in which disease
occurs and presents.

34. .
In the Laboratory:
• Mostly experimental
• Variables controlled by the investigator
• All variables known
• Replication easy
• Results valid
• Meaning of results in vivo uncertain.
• Little need for statistical manipulation
of data.
• Highly equipment intensive
In the Field:
 Mostly observational
 Variables controlled by nature
 Some variables unknown
 Replication difficult; exact
replication impossible
 Results often uncertain
 Meaning of results in vivo clear
 Statistical control often very
important
 Highly labor intensive

35. Measurement of Mortality
death
Measurement of Morbidity
Incidence
prevalence

36. The proportion of a particular population found to be
affected by a medical condition (typically a disease or a
risk factor such as smoking or seat-belt use).
Arrived at by comparing the number of people found to
have the condition with the total number of people
studied.
Usually expressed as a fraction, as a percentage, or as the
number of cases per 10,000 or 100,000 people.

37.  Point prevalence is the proportion of a population that has the
condition at a specific point in time.
 Period prevalence is the proportion of a population that has the
condition at some time during a given period (e.g., 12 month
prevalence), and includes case already have the condition at the
start of the study period as well as those who acquire it during
that period.
 Lifetime prevalence is the proportion of a population that at
some point in their life (up to the time of assessment) have
experienced the condition.

38. The development of new cases of a disease that occur
during a specified period of time in previously disease-free
or condition-free (“at risk”) individuals
Although sometimes loosely expressed simply as the
number of new cases during some time period, it is better
expressed as a proportion or rate.

39.  Incidence proportion (also known as cumulative incidence) takes
the perspective of what happen over an accumulation of time. For
example, the incidence proportion is 28 cases per 1,000 persons per
two years, i.e. 2.8% per two years.
 The incidence rate Incidence rate takes perspective of what is
happening from moment to moment (or year to year), it is also known
as the incidence density rate or person-time incidence rate. In
the same example as above, the incidence rate is 14 cases per
1000 person-years.

40.  .
Recurrence

41.  Counts
 Refers to the number of cases of a disease or other health
phenomenon being studied
 Limited usefulness for epidemiologic purposes without
knowing size of the source population
 Proportions
 tells us the fraction of the population that is affected
Tools of Measurement

42.  Ratios
 Like a proportion, is a fraction, without a specified relationship between
the numerator and denominator
 Rates
 A ratio in which forms part of the denominator
 Epidemiologic rates contain the following elements:
• health issue frequency (in the numerator)
• unit size of population
• time period during which an event occurs
Tools of Measurement

43.  Endemic: (Greek "in, within“; demos "people") condition when infection is
constantly maintained at a baseline level in a geographic area without external
inputs
 Epidemic (from Greek ἐπί epi"upon or above" and δῆμος demos "people") is the
rapid spread of infectious disease to a large number of people in a given
population within a short period of time, usually two weeks or less.
 Pandemic (from Greek πᾶν pan "all" and δῆμος demos "people") is
an epidemic of infectious disease that has spread across a large region; for
instance multiple continents, or even worldwide.

44. Terminology
Endemic
Epidemic
Pandemic
Time Location

45. A disease or condition at involves many or an
excessive number of people at the same time
and the same place
The occurrence of a disease or condition at a
frequency that is unusual or unexpected
increase above background or endemic level

46. Requirements for an outbreak or epidemic:
Presence of an infected host or other source of
infection.
Adequate number of susceptible.
An effective method of contact for transmission
to occur.

47.  establishing existence of
outbreak
 preparing for fieldwork
 verifying the diagnosis
 defining & identifying
cases
 using descriptive
epidemiology
 developing hypotheses
 evaluating hypotheses
 refining the hypotheses
 implementing control and
prevention measures
 communicating findings

48.  the study of epidemics
 the study of the dynamic factors involved in the transmission of
infectious agents in populations
 the natural history of infectious disease
 how a disease spreads through groups or a population
 how a case of that disease develops in an individual

49. Sites or Portals of Exit or Entry:
 Respiratory
 Enteric or Gastrointestinal
 Skin: if skin barrier is penetrated
 Genitourinary
 Eye

50.  Direct Contact: Person (animal)-to-Person (animal)
 Indirect Contact: Droplet, Fomites, Other Vehicles
 Water and Food (Gastrointestinal Tract)
 Vector-borne: often insects
 Intrauterine or Transplacental
 Organ Transplants, Blood and Blood Products

51.  Infection: the growth/multiplication of a microbe in a host
 Infection does not always result in injury of the host (disease)
 Two main classes of infection by site:
 localized
 generalized (disseminated; systemic)

52.  Organism enters the body and reaches target site of infection
 Organism adheres to or enters host cells and multiplies at site
of infection
 Infection spreads within the site (e.g., respiratory tract;
intestines)
 Symptoms of illness appear
 Organism does not spread through the lymphatic system or
reach the bloodstream
 Infection subsides due to host defenses (e.g., immunity)
 Agent eliminated from the body; infected cells replaced; "cure"

53.  Organisms enter the body and reaches target site of initial infection
 Organisms enter host cells & multiply at initial site of infection
 Infection spreads within site and to other sites via tissues, lymphatic
system, bloodstream (bacteremia, viremia, etc.) and other routes
 Symptoms of illness may appear
 Organisms infect other organs, tissues and cells, spread via
bloodstream
 Symptoms of illness become severe
 Host defenses eliminate organisms leading to cure or disease
continues, possibly leading to irreversible damage or death

55.  Agent (Microbe) Factors
 Sources, Reservoirs, Transport and Persistence (in the Environment)
 Ability to Enter a Portal in the Human or Other Host
 Ability to Reach and Proliferate at Site(s) of Infection in the Host
 Excretion of the Agent from the Host
 Quantity and "Quality" (including virulence) of the Infectious

56.  Environmental Factors
 Reservoirs: where organisms can live, accumulate or persist outside of
the host of interest; could be another organism or the inanimate
environment.
 Vehicles: inanimate objects/materials by which organisms get from one
host to another; includes water, food, objects (called fomites) and
biological products (e.g., blood).
 Amplifiers: Types of reservoirs where organisms proliferate; often
applied to organisms transmitted by the airborne route.

57.  Environmental Factors
 Vectors: Living organisms bringing infectious
organisms to a host.
 Mechanical vectors: Microbes do not multiply in the
vector
 ex: biting insects infected with the infectious organism
Biological vectors: Microbes must propagate in the
vector before they can be transmitted to a host.

58.  Physical:
 temperature, relative humidity, sunlight, moisture content or water
activity, climate and weather, etc.
 Chemical and Nutritional:
 Antimicrobial chemicals, nutrients for microbial proliferation.
 Biological:
 Antagonistic activity by other organisms: antimicrobial agents,
parasitism, etc.; presence and state of a vector

59.  Opportunities for host exposure
 transmission routes
 host availability
 Susceptibility factors
 Quantity & quality of infectious organisms, including their virulence
 age
 immunity
 nutritional status
 immunocompetence and health status,
 genetics
 behavior (personal habits) of host.

60.  Probability of infection is dose-dependent
 Higher dose gives higher probability of infection and illness; dose-response
relationship
 Microbes differ in their infectivity
 Enteric and respiratory viruses are infectious at very low doses
 1 cell culture ID has high probability of infecting an exposed individual.
 Most enteric bacteria infectivity are at moderate (10s-100s of cells) to
high (1,000 cells) doses.
 Protozoa infectivity are at low doses
 ID50 at 1-10 cysts of Giardia lamblia or oocysts of Cryptosporidium.

61. Microbes differ in their ability to produce the
different outcomes of infection:
(i) infection without illness;
(ii) infection with illness; (with or without long-term
sequelae)
(iii) infection, illness and then death

62. Mortality:
 all cause / cause-specific
Morbidity
 Disease-specific indicators
 General indicators: clinic use hospitalization, medication use
Quality of life
 General / Disease-specific
Costs

63. Infection Illness
Death
Sequelae
S e c o n d a r y S p r e a d
Recovery

65. .
What you see is not all, there is
much more hidden you can’t see.

66.  Prevention of Environmental contamination
 Control of Intermediate host, vectors and reservoirs
 Control of internal parasites
 Control of arthropod pests
 Control and reducing the infection as soon as an outbreak occurs
 Isolation of infected animals
 Quarantine for newly purchased animals

67. Vaccination of farm animals
Deworming of animals
Elimination of carriers
Disposal of carcass
Disinfection of animal houses
Disinfection of pastures

68.  The premises (sheds, stables, and kennels) and pastures should be prevented
from contamination.
 Elimination of parasites from the host at the most appropriate time by use of
antiparasiticides thereby preventing pasture contamination.
 Destruction of adult parasites in hosts prevents expulsion of eggs or the larvae
and the associated contamination of the environment.
 Ovicidal drugs should preferably be used to destroy the eggs, thereby preventing
environmental contamination.

69.  Anthelmentic treatments prior to rainy seasons using larvicidal drugs will
prevent contamination of pastures at a time when conditions are becoming
favourable for egg and larval development.
 Proper faeces disposal will give satisfactory control of faecally transmitted
monoxenous parasites of animals.
 Faeces or litter may be heaped to destroy the eggs/oocysts of parasites.
 Pens and pastures should not be overstocked.
 Reducing the stocking rate can significantly reduce the parasite burden in
animals and the associated problem of contamination in sheds and pastures.

70.  Limiting the contact between intermediate and final hosts by improvements in
management.
 Direct action may be taken to reduce or eliminate intermediate host populations.
 Reduction in the number of snail intermediate host by chemical (molluscides) or
biological control (ducks, Maris species of snails).
 Reduction in the number of snail intermediate hosts by drainage, fencing and
other management practices.

71.  Reduction in the number of insect and tick vectors by chemical
(insecticides/acaricides), biological control (hymenopterous insects,
entomopathogenic fungi and Bacillus thuringiensis) and genetic control
(sterile male technique, chromosomal translocation).
 Use of vaccines (Tickgard) at appropriate times may control the vector
population.
 Destruction of reservoir hosts is important in controlling certain parasites,
e.g., rodents for Leishmania and antelopes for African trypanosomes.

72.  Ridding the animal of internal parasites by periodical deworming,
 Preventing infestation of animals by keeping premises free from
infective forms of parasite – disinfestations, and
 Elimination of intermediate hosts.

73.  Manure, filth, damp and dark corners, stagnant water etc. are all
favorite breeding places of insects and these places should be
concentrated for removal and cleaning periodically.
 Eggs of ticks and mites deposited in cracks and crevices in the
walls, floors and wood work of the animal houses should be
removed periodically.
 Periodical (once in April-June and once in July-September)
dipping or spraying of animals with suitable insecticides to
prevent lice, flies, fleas, mites and ticks on skin of animals.

74.  Inside of animal sheds should be scrubbed and cleaned daily to remove all
filth.
 Areas around animal sheds should also be kept dry and clean.
 Interior of animal sheds (roofs, walls and corners) should be cleared
regularly of cobwebs and spider webs and sprayed with insecticides at least
once in a month.
 Dusting of animals with DDT, lorexane, gammexane or with some patent
preparations available in the market can be tried to control cattle warble
flies, etc.
 If the herd is small, individual animals can be dusted by hand.

75.  For larger herds a gunny bag (or any other bag having sufficiently
large pores through which dusting powder can escape out) filled
with dusting powder can be hung at a convenient place and at a
convenient place and at a convenient height.
 Newer generation synthetic pyrethroids like Deltamethrin
(ButoxTM), Cypermethrin (Cyprol, Tikkil) etc. are available in the
market.
 Great care should be taken while using these chemicals and
manufacturer’s instructions regarding their usage should be
scrupulously followed.

76.  Segregate sick animals.
 Stop all animals, animal products, vehicles and persons coming
into and out of the farm.
 Call a veterinarian for advice, adopt containment vaccination.
 Avoid grazing in a common place.
 Ban all visitors to the farm.
 Provide foot dips containing disinfectants at the entry of the farm
and gear up sanitation and hygiene.

77.  Isolation means segregation of animals, which are known to be or
suspected to be affected with a contagious disease from the apparently
healthy ones.
 Segregated animals should be housed in a separate isolation ward situated
far away from the normal animal houses.
 The isolation ward should never be at a higher level than that of the
healthy shed.
 If a separate accommodation is not available the animals concerned should
be placed at one end of normal animals’ buildings, as far away from healthy
stock as practicable.

78.  Attendants working on sick animals and equipment such as
buckets, shovels etc. should not be used for healthy stock.
 If this is not practicable, the sick animals should be attended to
daily, after the healthy stock.
 After this, the equipment should be thoroughly disinfected before
they are used on healthy stock next day; the attendant too should
wash his hands and feet in antiseptic and discard the clothes in
which he worked.
 The isolated animals should be brought back into the herd only
when the outbreak ends and they are fully recovered.

79.  Quarantine is the segregation of apparently healthy animals
(especially animals being brought into the herd for the first time),
which have been exposed to the risk of infection from those
animals, which are healthy and unexposed to the risk of infection.
 The idea is to give sufficient time for any contagious disease that
the quarantine animals may be having, to become active and
obvious. Hence, the quarantined period depends on the
incubation period of a disease. But in practice a quarantine period
of 21 days covers almost all diseases.

80.  For rabies, the quarantine period should be about six months.
 During the quarantine period, animals should be thoroughly
screened for parasitic infestation by faecal examination and
de-worming carried out on the 23rd/24th day, if need be.
 The animals should also be subjected to dipping or spraying
on the 25th/26th day for removing ectoparasites if any.

81.  Vaccination is a practice of artificially building up in the animal body immunity
against specific infectious diseases by injecting biological agents called vaccines.
 The term vaccine is used to denote an antigen (substance form organisms)
consisting of a live, attenuated or dead bacterium, virus or fungus and used for
the production of active immunity in animals.
 The term also includes substances like toxins, toxoids or any other metabolites
etc. produced by microbes and used for vaccination.
 The farm animals and young ones should be vaccinated at regular intervals at
appropriate times.
 Vaccination should be done with consultation of veterinarians.

82.  The most suitable time of deworming is the early stages of infection when
the worm load is less.
 The local veterinarian should be consulted for all suggestions regarding
dewormers and deworming.
 In adult animals deworming is done on examination of dung.
 It is good to deworm adult females after parturition.
 Older stock can be dewormed at 4-6 months’ intervals.
 In places where heavy endo-parasite infestations are found (hot-humid
regions) it is advisable to deworm heifers twice a year up to 2 years of age.

83.  Common diseases for which carriers have been observed in farm
animals are Tuberculosis, Leptospirosis and Brucellosis.
 Carriers of diseases in the herd should be diagnosed and eliminated so
that the herd may be completely free from diseases
 Certain diagnostic screening tests can be used for spotting out carriers
animals in the herd. These tests should be periodically conducted on
all animals in the herd so that carriers can be diagnosed and culled.
 Some of the commonly used screening tests are tuberculin test, Johnin
test, agglutination test and test for detection of subclinical mastitis.

84.  Carcasses should never be disposed off by depositing them in or
near a stream of flowing water, because this will carry infections
to points downstream.
 An animal died of a infectious disease should not be allowed to
remain longer in sheds as biting insects, rodents, etc. can reach it.
 Unless approved by a veterinarian (even then, only in a
disinfected place) it is not safe to open carcasses of animals that
have died of a disease.
 All carcasses should be disposed pr0perly by burying or burning.

85.  Under ordinary conditions, daily scrubbing and washing of houses and the
action of sunlight falling in the houses are sufficient enough to keep them
moderately germ-free.
 But when a disease outbreak has occurred disinfection is a must and should
be carried out scrupulously.
 All floors, walls up to height of 1.5 m, interiors of mangers, water troughs
and other fittings and equipment in contact with animals be disinfected.
 The first step in disinfection of animal houses is removal of all filth, as the
power of disinfectants is greatly reduced in the presence of organic matter.

86.  Floors, walls up to height of 1.5 m interior of water troughs and
mangers should be well scrubbed and all dung, litter etc. should
be removed and stacked separately, where animals cannot reach.
 In case of an outbreak of anthrax, the dung, litter etc. should first
be disinfected in situ thorough sprinkling of suitable disinfectant.
If the floor is of earth, which is generally the case in Indian
villages, the top 10cm earth should be removed and disposed off
along with litter.
 After removal of filth, the place should be scrubbed and washed
with 4 per cent hot washing soda solution (i.e., 4 kg /100 liters).

87.  The approved disinfectant solution should then be coated
liberally over the place by sprinkling or preferably by spraying and
left so to act for 24 hours.
 After this period, the animal house should again be washed with
clean water and left to dry by wind and sunlight.
 The interior of water troughs and mangers should be
whitewashed. (Done even routinely at fortnightly intervals.)

88.  Removal of any obvious infective material, like carcass, aborted
foetus, dung etc. from over the pasture and prevention of animals
from grazing on the pasture under question for at least three to
four months.
 The pasture can be ploughed up and left fallow about 6 months
during which period the pathogens would be destroyed by sun.

89.  Cross-sectional study
 A study that includes all persons, in the population, at the time of ascertainment, or
a representative sample of such persons. Disease and exposure are observed
simultaneously
 Cohort study
 Two groups (or more) groups of people that are free from the disease and that differ
according to the extent of their exposure to a potential cause of the diseases are
studied during a time interval.

90.  Case-Control study
 A case control study includes people with a disease and a suitable control group of
people unaffected by the disease.
 The occurrence of the possible cause (exposure) is compared between cases and
controls.
 A relevant situation is to think of a case-control study as a cohort study where
exposure is investigated for all cases and for a sample of the non-cases.